Cross-linked sulphonated polymers and their preparation process

ABSTRACT

The present invention is concerned with cross-linked sulfonated polymers, eventually perfluorinated, and their preparation process. When molded in the form of membranes, the polymers are useful in electrochemical cells, in a chlorine-sodium electrolysis process, as separator in an electrochemical preparation or organic and inorganic compounds, as separators between an aqueous phase and an organic phase, or as catalyst for Diels-Alder additions, Friedel-Craft reactions, aldol concentrations, cationic polymerization, esterification, and acetal formation.

This application is a divisional of U.S. patent application Ser. No.09/390,648, filed on Sep. 7, 1999 (pending), which is a continuation ofPCT Application PCT/CA99/00078, filed Jan. 29, 1999.

FIELD OF INVENTION

The present invention is concerned with cationic ion-exchange resins,particularly in the form of membranes, preferably partially orcompletely fluorinated, their applications, in particular inelectrochemical applications such as fuel cells, alkali-chlorideprocesses, electrodialysis, ozone production, as well as any otherapplication related to the dissociation of anionic centers linked to themembrane, such as heterogeneous catalysis in organic chemistry.

BACKGROUND OF THE INTENTION

Because of their chemical inertia, ion-exchange membranes partially orcompletely fluorinated are usually chosen for alkali-chloride processesor fuel cells consuming hydrogen or methanol. Such membranes arecommercially available under trade names like Nafion™, Flemion™, Dow™.Other similar membranes are proposed by Ballard Inc. in application WO97/25369 that describes copolymers of tetrafluoroethylene andperfluorovinylethers or trifluorovinylstyrene. The active monomers fromwhich these copolymers are obtained bear chemical functions that are theprecursors of ionic groups of the sulfonate or carboxylate type. Exampleof such precursors are:

wherein

X is F, Cl or CF₃;

n is 0 to 10 inclusively; and

p is 1 or 2.

Aromatic polymers of the polyimide or sulfonated polyether sulfone typehave also been considered, for example:

Once obtained, the copolymer containing the above precursors is molded,for example in the form of sheets, and converted into an ionic formthrough hydrolysis, to give species of the sulfonate or carboxylatetype. The cation associated to the sulfonate and carboxylate anioninclude the proton, an alkali metal cation (Li⁺, Na⁺, K⁺); analkaline-earth metal cation (Mg²⁺, Ca²⁺, Ba²⁺); a transition metalcation (Zn²⁺, Cu²⁺); Al³⁺; Fe³⁺; a rare earth cation (Sc³⁺, Y³⁺, La³⁺);an organic cation of the “onium” type, such as oxonium, ammonium,pyridinium, guanidinium, amidinium, sulfonium, phosphonium, theseorganic cations being optionally substituted by one or more organicradicals; an organometallic cation such as metallocenium,arene-metallocenium, alkylsilyl, alkylgermanyl or alkyltin.

Such membranes suffer from many important disadvantages.

A) Although the copolymers forming the membrane are insoluble in theirionic form, the membrane does not have a good dimensional stability andswells significantly in water or polar solvents. These copolymers forminverted micellia only when heated at high temperatures in a specificmixture water-alcohol that, after evaporation, allows the production ofa film. However, this film regenerated in the solid form does not havegood mechanical properties.

B) Tetrafluoroethylene (TFE) is a hazardous product to handle, becauseits polymerisation is performed under pressure and can causeuncontrolled reactions, particularly in the presence of oxygen. Becauseof the difference of boiling points between the two monomers forming thecopolymer, as well as their polarity difference, it is difficult toobtain a statistical copolymer corresponding to the addition rate ofeach monomer.

C) The ionic groups in high concentration on the chain have a tendencyto cause solubilisation of the copolymer. To prevent this phenomenon,the concentration of ionic groups is kept fairly low by adding animportant molar fraction of TFE monomers and/or by increasing thesecondary chains length (n>1), with the end result that theconcentration of the exchangeable ion groups are less than 1milliequivalent per gram. Consequently, the conductivity is relativelylow and highly sensitive to the water content of the membrane,particularly when the latter is acidified for applications in a fuelcell.

D) The penetration of methanol and oxygen through the membrane is high,because the perfluorocarbonated portion of the polymer allows an easydiffusion of the molecular species, which will chemically react at theopposite electrode and cause a loss of faradic efficiency, mainly inmethanol fuel cells.

Non-fluorinated systems like sulfonated polyimides or sulfonatedpolyether sulfones have the same drawbacks because one must compromisebetween the charged density, and thus the conductivity, and thesolubility or excessive swelling.

SUMMARY OF THE INVENTION

The present invention concerns a sulfonated polymer comprising afraction or all the sulfonyl groups cross-linked, and wherein at leastone fraction of the cross-linking bonds bear an ionic charge. Morespecifically, the cross-linking bonds are of the type:

P—SO₂—Y⁻(M⁺)—SO₂—P′

P—SO₂(M⁺)Y⁻SO₂—(Q—SO₂)_(r)Y⁻(M⁺)SO₂—P′

wherein

P and P′ are the same or different and are part of a polymeric chain;

Y comprises N or CR wherein R comprises H, CN, F, SO₂R³, C₁₋₂₀ alkylsubstituted or unsubstituted; C₁₋₂₀ aryl substituted or unsubstituted;C₁₋₂₀ alkylene substituted or unsubstituted, wherein the substituentcomprises one or more halogen, and wherein the chain comprises one ormore substituent F, SO₂R, aza, oxa, thia ou dioxathia;

R³ comprises F, C₁₋₂₀ alkyl substituted or unsubstituted; C₁₋₂₀ arylsubstituted or unsubstituted; C₁₋₂₀ alkylene substituted orunsubstituted, wherein the substituent comprises one or more halogens;

M⁺ comprises an inorganic or organic cation;

Q comprises a divalent radical C₁₋₂₀ alkyl, C₁₋₂₀ oxaalkyl, C₁₋₂₀azaalkyl, C₁₋₂₀ thiaalkyl, C₁₋₂₀ aryl or C₁₋₂₀ alkylaryl, each beingoptionally substituted by one or more halogens, and wherein the chaincomprises one or more substituents oxa, aza or thia; and

r is 0 or 1.

In a preferred embodiment, M+ comprises the proton, a metal cation, anorganometallic cation or an organic cation, the latter 2 optionallysubstituted with one or more organic radicals comprising:

a proton, an alkyl, an alkenyl, an oxaalkyl, an oxaalkenyl, an azaalkyl,an azaalkenyl, a thiaalkyl, a thiaalkenyl, a dialkylazo, a silaalkyloptionally hydrolysable, a silaalkenyl optionally hydrolysable, eachbeing straight, branched or cyclic and comprising from 1 to 18 carbonatoms;

a cyclic or heterocyclic aliphatic radical comprising from 4 to 26carbon atoms optionally comprising at least one lateral chain comprisingone or more heteroatoms such as nitrogen, oxygen or sulfur;

an aryl, an arylalkyl, an alkylaryl and an alkenylaryl of from 5 to 26carbon atoms optionally comprising one or more heteroatoms in thearomatic nucleus or in a substituent.

The metal preferably comprises an alkaline metal, an alkaline-earthmetal, a rare earth or a transition metal; the organometallic cationcomprises a metallocenium, an arene-metallocenium, an alkylsilyl, analkylgermanyl or an alkyltin, and the organic cation comprises R″O⁺(onium), NR″⁺ (ammonium), R″C(NHR″)₂ ⁺ (amidinium), C(NHR″)₃ ⁺(guanidinium), C₅R″N⁺ (pyridinium), C₃R″N₂ ⁺ (imidazolium), C₂R″N₃(triazolium), C₃R″N₂ ⁺ (imidazolinium), SR″⁺ (sulfonium), PR″⁺(phosphonium), IR″⁺ (iodonium), (C₆R″)₃C⁺ (carbonium), wherein R″ isdefined as an organic radical as defined above, and when an organiccation comprises at least two radicals R″ other than H, these radicalscan form together a cycle, aromatic or not, eventually containing thecenter bearing the cationing charge.

In a further preferred embodiment, the divalent radical Q and thesulfonated polymer are partially or completely fluorinated.

The present invention further comprises a process for cross-linkingsulfonyl groups of a sulfonated polymer wherein at least a fraction ofthe cross-linking bonds bear an ionic charge, the process comprisingmixing the polymer with a cross-linking agent allowing the reactionbetween 2 sulfonyl groups from adjacent polymeric chains, to form thesaid cross-linking bonds. Preferred cross-linking agents are of formula

(M⁺)A₂Y⁻;

(M⁺)AY⁻SO₂Y⁻A(M⁻);

(M⁻)AY⁻SO₂QY⁻A(M⁺)

wherein Y, Q and M are as defined above, and A comprises Si(R′)₃,Ge(R′)₃ or Sn(R′)₃ wherein R′ is C₁₋₁₈ alkyl.

DETAILED DESCRIPTION OF THE INVENTION

It is well known that perfluorinated polymers cannot usually becross-linked by conventional techniques used for non-fluorinatedpolymers because of the easy elimination of the fluoride ion and thesteric hindrance of the perfluorinated chains. However, the presentinvention describes a novel general technique to create cross-links,i.e., bonds, between sulfonyl groups attached to adjacent polymericchains, including those with a perfluorinated skeleton, for examplethose derived from monomer (I) and its copolymers:

Advantageously, the cross-linking can be performed when the polymer isin the form of a non-ionic polymer precursor, but after having beenmolded in the desired form. The end result is therefore a materialhaving enhanced mechanical resistance. The present invention alsoconcerns the molding of the cross-linked polymer in the form of amembrane or hollow fibers, (hereinafter “membranes”) for use in a fuelcell, a water electolyser, an alkali-chloride process, electrosynthesis,water treatment and ozone production. The use of the cross-linkedpolymers as catalysts for certain chemical reactions, because of thestrong dissociation of the ionic groups introduced by the cross-linkingtechnique and the insolubility of the polymeric chain, are also part ofthe invention.

The creation of stable cross-links is performed by a reaction betweentwo —SO₂Y groups from adjacent polymeric chains. The reaction isinitiated by a cross-linking agent, and allows the formation ofderivatives of the following forms:

wherein r, M, Y and Q are as defined above;

A comprises M, Si(R′)₃, Ge(R′)₃ or Sn(R′)₃ wherein R′ is C₁₋₁₈ alkyl;and

L comprises a leaving group such as a halogen (F, Cl, Br), anelectrophilic heterocyclic N-imidazolyl or N-triazolyl, R²SO₃ wherein R²is an organic radical as defined above.

The cation M⁺ can itself be solvated or complexed to increase itssolubility and/or its reactivity. For example, if M is a proton, thelatter can be complexed with the help of a tertiary base having a strongnucleophilic character, such as triethylamine, dimethylaminopyridine,1,4-diazabicyclo[2.2.2]octane, or in the form of a tertiobutyle radicalthat easily separates into a proton and CH₂═C(CH₃)₃. If M is a metallicion, the latter can be solvated by dialkylethers of oligo-ethyleneglycols, or methylated oligo-ethylenediamines.

Alternately, the cross-linking agent A₂Y⁻(M⁺) can be formed in situ inthe presence of a strong base, for example an organometallic or ametallic dialkyl amine such as diisopropylamide-lithium reacting on theleaving protons linked to the Y radical in the following manner:

HN[Si(CH₃)₃]₂+C₄H₉LiC₄H₁₀+LiN[Si(CH₃)₃]₂;

CH₂[Si(CH₃)₃]SO₂CF₃+2CH3MgClLi2CH₄+(MgCl)₂C[Si(CH₃)₃]SO₂CF₃

Preferred organometallic cross-linking agents include organo-lithium,organo-magnesium or organo-aluminium, that are also a carbon source whenY═CR, and amides and metallic nitrides as a nitrogen source when Y═N.

An advantage of the present invention is that the cross-linking agentsprovide negatively charged species that are bound to the sulfonyl groupsof the polymers, and used as bridges between adjacent polymeric chains.It is well known that sulfonylimide groups and di- or trisulfonylmethanegroups are strong electrolytes in most media, and therefore, thecross-linking reaction, in addition to improving the mechanicalproperties, does not have any detrimental effect on the conductivity. Infact, the latter is often increased.

The following compounds are preferred cross-linking ionogenes agents,i.e., ionic groups generators, when L is on the polymeric chain: Li₃N;C₃Al₄; [(CH₃)₃Si]₂NLi (or Na or K); NH₃+3 DABCO;CF₃SO₂C[(CH₃)₃Si][Li(TMEDA)]₂; (CH₃)₃CNH₂+3 TEA; NH₂SO₂NH₂+4 TEA;[[(CH₃)₃Si](Li)N]₂SO₂; [(TMEDA)(Mg)N]₂SO₂; CH₃Li; (CH₃)₃Al; NH₂Li (or Naor K); [[Si(CH₃)₃](Li)NSO₂]₂CF₂, [Li[Si(CH₃)₃]NSO₂CF_(2]) ₂CF₂;[(Li)Si(CH₃)₃NSO₂CF₂]; and [Li[Si(CH₃)₃]NSO₂CF₂CF₂]₂O, whereinTEA=triéthylamine; TMEDA=N,N,N′N′ tetramethylethylene diamine andDABCO=1,4-diazabicyclo-[2,2,2,]-octane.

Alternately, the cross-linking, reaction can take place when the Y groupis already on the precursor of the polymer, for instance in the case ofa substituted amide. In such a case, the general scheme is as follows:

The following compounds are examples of preferred ionogene cross-linkingagents when L is on the reagent: SO₂Cl₂+3 DABCO; SO₂(imidazole)₂;[FSO₂CF₂]₂+3 TEA; (ClSO₂CF₂)CF₂+3 DABCO and (FSO₂CF₂CF₁)₂O+3 DABCO.

The cross-linking reaction may imply all the sulfonyl groups, or only afraction thereof. These cross-linking reagents can be added or usedaccording to various techniques well known to those skilled in the art.Advantageously, the polymer is molded in the desired form prior to thecross-linking, for example in the form of a membrane or a hollow fiber,and the material is immerged or covered with a solution of thecross-linking agent in one or more solvent favoring the couplingreaction. Preferred solvents are polyhalocarbons, tetrahydrofuran (THF),glymes, tertiary alkylamides such as dimethylformamide,N-methylpyrrolidone, tetramethylurea and its cyclic analogues,N-alkylimidazoles, and tetraalkylsulfamides. The desired cross-linkingdegree can be controlled through various factors, such as the time ofimmersion in the solvent containing the cross-linking agent, thetemperature of the solvent, the concentration of the cross-linking agentin the solvent, or a combination thereof. Preferably, these parametersare adjusted to produce the desired properties in a relatively shortperiod of time varying between a few seconds to about ten hours, and thetemperatures are chosen to be compatible with the usual solvents, from−10° C. to 250° C. For comparison purposes, hydrolysis of a Nafion®membrane takes more than 24 hours for usual thicknesses.

Alternately, a latex of the polymer to be molded is mixed preferably inthe presence of fluids that are not solvents, such as ordinary orfluorinated hydrocarbons, with the solid cross-linking agent, and themixture is heat pressed or calendered. This technique can be appliedadvantageously to thin membranes, and provides high productivityeventhough it is possible that the membrane be less homogeneous.Reinforcing agents such as fillers, organic or inorganic, like powders,fibers or strands woven or not, can be added to the polymers before thecross-linking reaction to reinforce the structure. Also, agents creatingof porosity can be incorporated if necessary to increase the exchangesurfaces with external fluids (catalytic purposes).

If only a fraction of the links bridging the polymeric chains arerequired, the remaining SO₂Y groups can be hydrolysed conventionally inthe sulfonate form by alkaline hydrolysis. Alternately, in a preferredembodiment, the sulfonate group —SO₃ ⁻M⁺ and the non cross-linked groups—SO₂NSO₂R_(F) ⁻M⁺ or —SO₂C(R)SO₂R_(F) ⁻M⁺ wherein R_(F) comprises anorganic radical preferably halogenated, particularly fluorinated, can beobtained in the same conditions as for the cross-linking reactions fromnon cross-linking ionogene agents such as M[(CH₃)₃SiO],M[(CH₃)₃SiNSO₂R_(F)] or M[(CH₃)₃SiC(R)SO₂R_(F)], or any other agentcapable of introducing —NSO₂R_(F) or C(R)SO₂R_(F) groups as areplacement for Y. It can be advantageous to treat the membranesequentially with the cross-linking agent, and then with the noncross-linking ionogene agent. Alternately, the cross-linking agent andin the non cross-linking ionogene agent are mixed and dissolved in asolvent in predetermined concentrations, so that they can reactsimultaneously.

The cross-linked polymer obtained in accordance with the process of thepresent invention can be easily separated from the secondary products ofthe reaction, that are volatile, such as (CH₃)₃SiF or (CH₃)₃SiCl.Alternately, the cross-linked polymer can be washed with an appropriatesolvent such as water or an organic solvent wherein it is insoluble.Further, conventional techniques well known to those skilled in the art,for example ion exchange or electrophoresis, can be used to change thecation M⁺ obtained in the cross-linking reaction and/or coming from thenon cross-linking ionogene agent, by the desired cation for the finalapplication.

The following examples are provided to illustrate the invention andshould not be considered as limiting its scope.

EXAMPLE 1

15 g of polyethersulfone in the powder form are sulfonated with 11 g ofchlorosulfonic acid in 75 ml of 1,2-dichloroethane. The concentration ofthe sulfonic groups reaches 0.47 units SO₃H per aromatic nucleus. SO₃Hgroups are transformed in SO₂Cl groups by adding an excess ofchlorodimethylaminium chloride in DMF. The polymer in the form of apowder is filtered and washed with anhydrous acetonitrile and driedunder vacuum. Under an anhydrous atmosphere, the polymer in thechlororosulfonated form is molded in the form of a film by pressing andcalendering at 150° C. A film of a thickness of 50 microns is cut insquares of 4 cm sides, and immersed in a solution of 0.6 g. of thelithiated derivative of hexamethyl-disilazane Li[N(Si(CH₃)₃)₂] in 50 mlof dimethylethyleneurea (DMEU). The polymer is treated in theseconditions for one hour at 110° C. under dry argon atmosphere. Themembrane is removed from the reaction medium, rinsed with THF andtreated with an excess of lithium trimethylsilanoate (1 g) in 50 ml of1,2-dimethoxyethane under argon for 24 hours at 25° C. The membrane isrinsed several times with distilled water, and the metallic ions areexchanged with protons in a Soxhlet extractor with a hydrochloric acidsolution at an azeotropic concentration in water (i.e., 20.2% byweight). The membrane thus obtained has a conductivity greater than 10⁻³Scm⁻¹ at 25° C. and 95% relative humidity. 24% of the sulfonyl groupsare engaged in the formation of imidide bridges and the membrane doesnot show noticeable dimensional variations in the various solventstested, which include water, methanol, ethanol, acetonitrile andpropylene carbonate.

EXAMPLE 2

A commercial membrane of Nafion 117® of 175 μm thickness in the form ofa lithium salt is dried and cut in slices of 4 cm×10 cm. The membranespiraly rolled up is treated with 2 g of sulfur dimethylaminotrifluoride(CH₃)₂NSF₃ in 50 ml of THF under reflux, then rinsed. The polymer nowcontaining sulfonated groups in the form SO₂F is immersed in a solutionof 60 mg of the hexamethydisilazane sodium salt in 20 ml of anhydrousdiglyme and refluxed under argon. After 3 hours, the membrane is removedfrom the reaction media, rinsed with THF and treated with a solution of500 mg of sodium trimethysilanoate in the same solvent. After 48 hours,the membrane is washed with water and ethanol, and transformed in thehydronium salt by several successive immersions in a nitric acidsolution 2 M in water at 60° C. High resolution solid NMR shows that 32%of the sulfonyl group of the membrane are in the sulfonimide form and78% in the sulfonate form. The increase of volume of the membrane in thepresence of water or methanol when immersed in these solvents, includingat the boiling point, is lower than 10%.

EXAMPLE 3

A copolymer of tetrafluoroethylene in perfluorovinyloxyethane-sulfonylefluoride containing 35% molar of the sulfonated monomer is heatcalendered to form a 20 microns thick film. The compound[Na(Si(CH₃)₃NSO₂CF₂]₂CF₂ is prepared from thehexafluoropropane-1,3-disulfonic acid fluoride according to thefollowing sequence of reactions:

[FSO₂CF₂]₂CF₂+6 NH₃2NH₄F+[NH₄)HNSO₂CF₂]₂

[(NH₄)HNSO₂CF₂]₂+Na₂CO₃[(Na)HNSO₂CF₂]₂+2NH₃+H₂O+CO₂

[(Na)HNSO₂CF₂]₂+HN[(Si(CH₃)₃]₂Na[Si(CH₃)₃NSO₂CF₂]₂CF₂+NH₃

10 square sections of 10 cm×10 cm of this membrane separated bypolypropylene wire-mesh, are immersed in a glass recipient and coveredwith a solution of 600 mg of the sulfamide disodic derivative in 50 mlin diglyme. The mixture is heated to 125° C. for 4 hours under argon.The membranes are then immersed in a solution of 1 g of lithiumhydroxide LiOH in 50 ml of methanol, and hydrolysis of the residual SO₂Ffunctions into sulfonate groups is continued at 50° C. for 4 hours. Thecross-linked membrane is washed with deionised water, and the sodiumions are exchanged with protons by nitric acid 2M. The membrane is keptunder air after deionized water rinsing.

The compounds [FSO₂CF₂]₂O, [FSO₂CF₂CF₂]₂O, and [ClSO₂CF₂CF₂]CF₂ cansimilarly be substituted to the hexafluoropropane-1,3-disulfonic acidfluoride as precursors of the bridging agent.

EXAMPLE 4

A membrane of 20 μm of the copolymer of tetrafluoroethylene andperfluorovinyloxyethanesulfonyl fluoride of Example 3 is treated in asolution of 800 mg of the sulfamide disodic derivative of Example 3 and400 mg of sodium trimethylsilanoate in 50 ml of diglyme. The mixture isheated at 125° C. for 4 hours under argon. The membrane is removed andwashed with deionized water and exchanged with protons as described inExample 3.

EXAMPLE 5

A copolymer of tetrafluoroethylene and perfluorovinyloxyethanesulfonylfluoride at 35% molar of sulfonated monomer of Example 3 is cross-linkedin a similar manner by immersion in the bridging agent[Na(Si(CH₃)₃NSO₂CF₂]₂CF₂ in the conditions of Example 3. The membranethus cross-linked and containing residual groups —SO₂F is treated with 3g of the sodium salt of the trifluoromethanesulfonamide derivative offormula Na[Si(CH₃)₃NSO₂CF₃] in diglyme at 110° C. The membrane is rinsedand the sodium ions are exchanged with protons with nitric acid 2M. Allthe sulfonated functions of the membrane are in the form of bridging orfree sulfonamide groups:

P—SO₂N(H)SO₂(CF₂)₃SO₂N(H)SO₂—P

P—SO₂N(H)SO₂(CF₃)

wherein P represents the polymeric chain.

EXAMPLE 6

A copolymer of tetrafluoroethylene and perfluorovinyloxyethanesulfonylfluoride similar to that prepared in Example 3 and containing 35% ofsulfonated monomer is mixed while hot with a powder of sodium chloridehaving a particle size lower than 2 microns and a volume fraction of45%, and then granulated at a particle size of about 25 microns ofdiameter. 5 g of this composite copolymer are treated with 2 g of thehexamethyldisilazane sodic derivative in 30 ml of diglyme at 125° C. for3 hours and the residual SO₂F functions are reacted with the sodium saltof the trifluoromethanesulfonamide derivative formulaNa[Si(CH₃)₃NSO₂CF₃] in diglyme at 125° C. After washing with water andremoval of the sodium chloride acting as a porophore, i.e., creatingporosity after its elimination, the polymer presents itself in the formof granules having high specific surface area allowing a quick access tothe ionic sites.

EXAMPLE 7

The compound [CF₃SO₂C(MgCl)₂SO₂CF₂]₂CF₂ is prepared from thehexafluoropropane-1,3-disulfonic acid fluoride according to thefollowing reactions sequence:

[FSO₂CF₂]2CF₂+2CF₃SO₂CH₃+4LiH→2H₂+[CF₃SO₂CH(Li)SO₂CF₂]₂CF₂

[CF₃SO₂CH(Li)SO₂CF₂]₂CF₂+2C₄H₉Li+4MgCl₂?

[CF₃SO₂C(MgCl)₂SO₂CF₂]₂CF₂+2C₄H₁₀+2LiCl

The sequence of reactions is performed in the same recipient (“one pot”synthesis) in the dibutylether of diethylene glycol (Ferro, USA). Amembrane of a thickness of 20 microns and a size of 10 cm×10 cm preparedfrom the copolymer of Example 3 is immersed in a solution of 200 mg, ofchloromagnesium tetrasalt of tetrasulfone in 30 ml of anhydrousdibutylether of diethylene glycol. The reaction is performed underdeoxygenated nitrogen at 110° C. for 6 hours. The membrane is removedfrom the reaction medium, rinsed with THF and hydrolysis of the residualSO₂F groups is performed as above with lithium trimethylsilanoate. Themembrane is washed and exchanged with protons in the same conditions asin Example 3. The compounds [FSO₂CF₂]₂O, [FSO₂CF₂CF₂]₂O, and[ClSO₂CF₂CF₂]CF₂ can be similarly substituted to thehexafluoropropane-1,3-disulfonic fluoride as precursors of the bridgingagent.

EXAMPLE 8

A polymer of 4-trifluorovinyl-benzenesulfonyle fluoride is prepared byradicalar initiation with benzoyl peroxide in dimethylformamide. Thepolymer is precipitated in ether. A solution of 12% of this polymer incyclopentanone is spread and the solvent is dried under dry air. Thepolymeric film obtained has a thickness of 24 microns. 100 cm² of thismembrane are immersed in a mixture of 200 mg of the sodium salt ofhexamethyldisilazane and 100 mg of sodium trimethylsilanoate in 10 ml ofa mixture o-xylene/diglyme (50:50 v/v). The reaction medium ismaintained at 80° C. for 10 hours and the side products of the reactionare eliminated by successive washings with THF, methanol and water. Theion exchange of lithium with protons gives a material having aconductivity greater than 10⁻² Scm⁻¹ à 95% relative humidity.

EXAMPLE 9

The poly(4-trifluorovinylbenzenesulfonyl fluoride) of Example 7 isspread in the form of a solution on a polypropylene support to form a 35micron thick film, that is subsequently cut into a membrane of 1meter×10 cm of side. This membrane spirally rolled up with a stainlesssteel wire-mesh allows access to all the surface of the membrane. Thisassembly is placed in a 100 ml reactor to which are added 2 ml of asolution of 0.5 M ammonia in dioxanne and 700 mg de DABCO(1,4-diazabicyclo-[2,2,2,]-octane) in 80 ml of dimethoxyethane. Thereactor is closed and maintained at 115° C. for 4 hours under autogenicpressure. After cooling and restoration of ambient pressure, themembrane is separated from the reaction medium and hydrolysis of theresidual SO₂F groups is performed with a solution of 5 g of caustic sodain an ethanol-water mixture (80:20 v/v). The protonic exchange isrealized in the same conditions as those of Example 8.

EXAMPLE 10

10 g of a copolymer of tetrafluoroethylene andperfluorovinyloxyethanesulfonyl fluoride containing 28% molar of thesulfonate monomer obtained in the form of a latex by emulsionpolymerisation in 300 mg of lithium nitride in the powder form(submicronic size) are dispersed in a blender in 50 ml of FluorinertFC-75® (3M, USA). The suspension is spread on a stainless steel sheet ofa thickness of 25 microns, and the solvent is evaporated to give a 30microns thick film that is subsequently coated with a further stainlesssteel sheet. The fluorinated polymer is cross-linked by heat pressing at100 Kg.cm⁻² and 150° C. for 1 hour. The cross-linking reaction orbridging between the —SO₂F functions is achieved according to thefollowing equation:

2-SO₂F+Li₃N2LiF+—SO₂N(Li)SO₂F—

After separation of the sheets, the residual SO₂F functions arehydrolyzed with an aqueous solution of lithium hydroxide, and severalwashings with water allow the elimination of lithium fluoride, which isa by-product of the cross-linking reaction or hydrolysis of the SO₂Fgroups. The membranes are exchanged with protons by several immersionsin nitric acid 2M à 60° C.

The same cross-linking process can be applied by replacing lithiumnitride with aluminum carbide (240 mg for 10 g) to obtain sulfonebridges.

EXAMPLE 11

A membrane of the copolymer of the tetrafluoroethylene andperfluorovinyloxyethanesulfonyl fluoride similar to that of Example 3 isimmersed in a solution of 0.5 M ammonia in dioxanne and left to reactfor 48 hours. The SO₂F groups are transformed into —SO₂NH(NH₄) groupsfrom which the sulfonamide is obtained by treatment with a hydrochloricacid solution, and rinsed. The sodium salt is obtained by immersion in10% sodium carbonate solution, followed by rinsing with deionized water.The polymer is dried under vacuum, and 100 cm² of the membrane areimmersed in an hexamethydilsilazane solution in acetonitrile, andrefluxed for 48 hours. After separation from the reaction medium anddrying, the membrane is placed in a reactor containing 100 ml ofacetonitrile and 300 mg of hexafluoropropane-1,3-disulfonic acidfluoride [FSO₂CF₂]₂CF₂, and the reactor is closed and heated at 110° C.for 2 hours. After cooling, the membrane is removed and the remaining—SO₂F groups are hydrolyzed with a caustic soda solution in a mixturewater-alcohol (50:50 v/v) under reflux. The sodium ions are exchangedwith the protons in a manner similar to that of the preceding exampleswith nitric acid 2M.

In a variation, the sulfonamide functions —SO₂NH₂ are treated with anexcess of dibutyl-magnesium, the membrane is rinsed in anhydrous THF andput in a solution of [FSO₂CF₂]₂CF₂ at room temperature. In both methods,the compounds [FSO₂CF₂]₂O, [FSO₂CF₂CF₂]₂O and [ClSO₂CF₂CF₂]CF₂ can besubstituted to the hexafluoropropane-1,3-disulfonic acid fluoride.

EXAMPLE 12

An experimental fuel cell is made from a membrane obtained according toExample 3. A nanometric dispersion of platinum on a carbon support(Degussa) is applied on each side of the membrane through a serigraphytechnique from a dispersion of platinated carbon in a colloidal solution(5% w/w) of Nafion 117® (in a mixture of light alcohols (Aldrich). Thesystem is treated at 130° C. to ensure cohesion of the Nafion®particles. The current collectors are made of grooved graphite plates toensure the distribution of the gases. The experimental cell is testedwith hydrogen and oxygen feeding at ambient pressure. The tension inopen circuit is 1.2 V and the current-tension curve measured on thisassembly indicates that 500 mA/cm² are obtained at a tension of 0.65 V.The replacement of platinum in the negative electrode with an alloy ofplatinum-ruthenium 50:50 allows the use of methanol as the fuel with acurrent density of 150 mA/cm² at a tension of 0.6 V. Permeation ofmethanol in these conditions is less than 5 μmoles/cm²·s¹.

EXAMPLE 13

An experimental fuel cell is made from a membrane obtained according toExample 9 in the form of —SO₂F precursors. The platinated carbonelectrode of Example 11 is applied on each side of the membrane throughserigraphy of a suspension of this material in a solution of thepoly(trifluoromethylstyrenesulfonyl) fluoride in 1,2-dichloroethane.Cross-linking of the —SO₂F functions of the complete system is, in thesame manner as in Example 7, performed by reacting a mixture of thesodic derivative of hexamethyldisilazane and sodium trimethylsilanoatein 10 ml of a mixture o-xylene/diglyme (50:50 v/v). After cross-linking,the Na⁺ ions of the membrane and the electrodes binder are exchanged byprotons with concentrated hydrochloric acid, and rinsing. Theexperimental fuel cell using this assembly has performances similar tothose obtained for the cell described in Example 12.

EXAMPLE 14

Electrolysis of sodium chloride is performed in a cell having twocompartments separated by a membrane prepared according to Example 3,the anode being of the type DSA (“dimensionally stable electrode”) andmade of titanium coated with a layer of ruthenium oxide RuO₂, in contactwith the membrane, the cathode being made of nickel. The ohmic drop for2 A/cm² is 0.4V and the permeation of OH⁻ ions through the membrane islower that 8.5 μmoles/cm²·s¹.

EXAMPLE 15

The membrane prepared according to Example 4 is used for the preparationof ozone by water electrolysis on a lead dioxide anode. The cathode is agrid of platinum, both electrodes being plated on the membrane havingthe cathodic side immersed in water. The zone faradic yield is 20% under4.5 V.

EXAMPLE 16

The porous ion exchange resin prepared in Example 5 is used as achemical reaction catalyst. In the active protonic form afterdehydration under vacuum, the resin catalyses Friedel-Craft reactions,esterifications, acetalisations etc. To an equimolecular mixture ofanisole and acetic anhydride are added 3% by weight of the resin in theacidic form. The formation reaction of the 4-methoxyacetophenone iscompleted in 45 minutes at room temperature.

The proton exchange for the transition ions and the rare earth metals,in particular La⁺³ and Y⁺³, provide a catalyst for the Friedel-Craftreactions and the cross-aldolisation.

To an equimolecular mixture of cyclopentadiene and vinyl-methyl ketone(10 mmoles in 30 cc of dichloromethane) are added 5% by weight of theresin in the form Y⁺³ dried under vacuum at 60° C. The formationreaction of the Diels-Alder condensation compound is completed at à 25°C. in 30 minutes, the endo/exo ratio being close to 90:10.

In both cases, the catalyst is eliminated by simple filtration, and isreusable.

Wile the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications, and this application is intended to cover any variations,uses or adaptations of the invention following, in general, theprinciples of the invention, and including such departures from thepresent description as come within known or customary practice withinthe art to which the invention pertains, and as may be applied to theessential features hereinbefore set forth, and as follows in the scopeof the appended claims.

What is claimed is:
 1. Process for cross-linking sulfonyl groups of asulfonated polymer wherein at least a fraction of the cross-linkingbonds bear an ionic charge, the process comprising contacting thepolymer with the cross-linking agent allowing the reaction between twosulfonyl groups from adjacent polymeric chains to form the cross-linkingbonds, wherein the cross-linking bonds are of the type:P—SO₂—Y⁻(M⁺)—SO₂—P′; or P—SO₂(M⁺)Y⁻SO₂—(Q—SO₂)_(r)—Y⁻(M⁺)SO₂—P′ whereinP and P′ are the same or different and are part of a polymeric chain; Ycomprises N or CR wherein R comprises H, CN, F, SO₂R³, C₁₋₂₀ alkylsubstituted or unsubstituted; C₁₋₂₀ aryl substituted or unsubstituted;C₁₋₂₀ alkylene substituted or unsubstituted, wherein the substituentcomprises one or more halogen, and wherein the substituted chaincomprises one or more substituent F, SO₂R, aza, oxa, thia or dioxathia;R³ comprises F, C₁₋₂₀ alkyl substituted or unsubstituted; C₁₋₂₀ arylsubstituted or unsubstituted; C₁₋₂₀ alkylene substituted orunsubstituted, wherein the substituent comprises one or more halogens;M⁺ comprises an inorganic or organic cation; Q comprises a divalentradical C₁₋₂₀ alkyl, C₁₋₂₀ oxaalkyl, C₁₋₂₀ azaalkyl, C₁₋₂₀ thiaalkyl,C₁₋₂₀ aryl or C₁₋₂₀ alkylaryl, each being optionally substituted by oneor more halogens, and wherein the chain may comprise one or moresubstituents oxa, aza, or thia; r is 0 or 1; and the divalent radicaland the sulfonated polymer are partially or completely fluorinated. 2.Process according to claim 1 wherein M⁺ comprises the proton, a metalcation, an organometallic cation or an organic cation optionallysubstituted with one or more organic radicals comprising: a proton, analkyl, an alkenyl, an oxaalkyl, an oxaalkenyl, an azaalkyl, anazaalkenyl, a thiaalkyl, a thiaalkenyl, a dialkylazo, a silaalkyloptionally hydrolysable, a silaalkenyl optionally hydrolysable, eachbeing straight, branched or cyclic and comprising from 1 to 18 carbonatoms; a cyclic or heterocyclic aliphatic radical comprising from 4 to26 carbon atoms optionally comprising at least one lateral chainoptionally comprising one or more heteroatoms such as nitrogen, oxygenor sulfur; or an aryl, an arylalkyl, an alkylaryl and an alkenylaryl offrom 5 to 26 carbon atoms optionally comprising one or more heteroatomsin the aromatic nucleus or in a substituent.
 3. Process according theclaim 1 wherein the metal comprises an alkaline metal, an alkaline-earthmetal, a rare earth or a transition metal; the organic metallic cationcomprises metallocenium, an arene-metallocenium, an alkylsilyl, analkylgermanyl or an alkyltin, and the organic cation comprises an oniumselected from the group consisting of oxonium, ammonium, amidinium,guanidinium, pyridinium, imidazolium, triazolium, imidazolinium,sulfonim, phosphonium, iodonium, and carbonium wherein the oniumcomprises at least one organic radical R″ and when an organic cationcomprises at least two radicals R″ different from H, these radicals canform together a cycle, aromatic or not, eventually containing the centerbearing the cationic charge.
 4. Process according to claim 1, wherein aleaving group is linked to the sulfonyl groups before performing thecross-linking.
 5. Process according to claim 4 wherein the leaving groupcomprises F, Cl, Br, an electrophilic heterocycle N-imidazolyl,N-triazolyl, R²SO₃, R² being an organic radical optionally halogenated,the organic radical comprising: a proton, an alkyl, an alkenyl, anoxaalkyl, an oxaalkenyl, an azaalkyl, an azaalkenyl, a thiaalkyl, athiaalkenyl, a dialkylazo, a silaalkyl optionally hydrolysable, asilaalkenyl optionally hydrolysable, each being straight, branched orcyclic and comprising from 1 to 18 carbon atoms; a cyclic orheterocyclic aliphatic radical comprising from 4 to 26 carbon atomsoptionally comprising at least one lateral chain optionally comprisingone or more heteroatoms such as nitrogen, oxygen or sulfur; an aryl, anarylalkyl, an alkylaryl and an alkenylaryl of from 5 to 26 carbon atomsoptionally comprising one or more heteroatoms in the aromatic nucleus orin a substituent.
 6. Process according to claim 1, wherein thecross-linking agent comprises an organometallic comprisingorgano-lithium, organo-magnesium, magnesium or organo-aluminum, or acompound of general formula: (M⁺)A₂Y⁻; (M⁺)AY⁻SO₂Y⁻A(M⁺); (M⁺)AY⁻SO₂QSO₂ Y⁻A(M⁺) wherein Y, Q and M are as defined above, and A comprises M,Si(R′)₃, Ge(R′)₃ or Sn(R′)₃ wherein R′ is C₁₋₁₈ alkyl.
 7. Processaccording to claim 6 wherein A comprises a trialkylsilyl group. 8.Process according to claim 6 wherein the cross-linking agent comprisesLi₃N; C₃Al₄; [(CH₃)₃Si]₂NLi (or Na or K); NH₃+3 DABCO;CF₃SO₂C[(CH₃)₃Si][Li(TMEDA)]₂; (CH₃)₃CNH₂+3 TEA; NH₂SO₂NH₂+4 TEA;[[(CH₃)₃Si](Li)N]₂SO₂; [(TMEDA)(Mg)N]₂SO₂; CH₃Li; (CH₃)₃Al; NH₂Li (or Naor K); [[Si(CH₃)₃](Li)NSO₂]₂CF₂; [Li[Si(CH₃)₃]NSO₂CF₂]₂CF₂;[(Li)Si(CH₃)₃NSO₂CF₂]; [Li[Si(CH₃)₃]NSO₂CF₂CF₂]₂O; SO₂Cl₂+3 DABCO;SO₂(imidazole)₂; [FSO₂CF₂]₂+3 TEA; (ClSO₂CF₂)₂CF₂+3 DABCO and(FSO₂CF₂CF₂)₂O+3 DABCO.
 9. Process according to claim 1 wherein the noncross-linked polymer is molded before being cross-linked.
 10. Processaccording to claim 1 wherein the non cross-linked polymer ismechanically blended with the cross-linking agent, pressed and heated.11. Process according to claim 1 wherein the non cross-linked polymer ismolded and contacted with a solution of the cross-linking agent in aninert solvent.
 12. Process according to claim 11 wherein thecross-linking density is controlled by the time of immersion in thesolvent, the temperature of the solvent, or the cross-linking agentconcentration in the solvent.
 13. Process according to claim 11 whereinthe solvent comprises aromatic hydrocarbons, hydrocarbons and aliphaticethers partially or completely halogenated, THF, alkylethers of mono-,di- tri- and tetraethylene glycols (glymes), tertiary alkylamidesincluding DMF, N-methylpyrrolidone, tetramethylurea and its cyclinganalogues, N-alkylimidazoles, tetraalkylsulfamides, and mixture thereof.14. Process according to claim 1 wherein the non cross-linked polymer ismolded and contacted with the cross-linking agent and the noncross-linking ionogene agent to form end groups —SO₃ ⁻(M⁺), or—[[SO₂YSO₂R]⁻(M⁺), R being an organic radical as defined above. 15.Process according to claim 14 wherein the non cross-linked polymer ismolded and contacted sequentially or simultaneously with thecross-linking agent and the non cross-linking ionogene agent. 16.Process according to claim 14 wherein the non cross-linking ionogeneagent comprises (CH₃)₃SiO⁻(M⁺) or [(CH₃)₃SiNSO₂RF]⁻(M⁺) wherein M⁺ is asdefined above and R_(F) is an alkyl, oxaalkyl, azaalkyl or thiaalkylradical essentially perfluorinated and comprising from 1 to 12 carbonatoms.
 17. Process according to claim 1 wherein a reinforcing agent isadded to the polymer before cross-linking.
 18. Process according toclaim 14, wherein R is halogenated.
 19. Process according to claim 18,wherein R is perfluorinated.